I think that is rather AL sociology problem that economy. People just sold credits "under table" to friends and gang members, or make agreements in forum rather that post them in market for anyone to buy
The high credit prices have nearly everything to do with Bigrod's hosp spree and credit buyout. The prices have rarely dropped below a buying price of 250. It's all about speculation right now. Why post your credits at $230 when people will buy them at $250?
Last week the average price for credits sold wasn't much different than the historical average. It's not that there aren't credits being posted, there is just a lot of demand at the moment. The cheaper postings are selling fast.